Multi-stage gas compressing apparatus

ABSTRACT

A compressed gas compressed by the first gas compressor is further compressed by the second gas compressor. The compressed gas from the first gas compressor is sent to a crank case of the second gas compressor in which the gas is further compressed. The gas is sent to a cylinder of the second gas compressor and compressed by a piston in the cylinder.

BACKGROUND OF THE INVENTION

The present invention relates to a multi-stage gas compressingapparatus, and particularly to a multi-stage gas compressing apparatusin which a compressed gas is compressed by a plurality of gascompressors gradually.

JP2003-97466A discloses an oilless gas compressor in which a compressedgas introduced in the cylinder from the inlet is compressed by thepiston which reciprocates with rotation of the crankshaft via theconnecting rod in the crank case and is discharged from the outlet intoa storage tank.

Nowadays, it is necessary to use an oilless compressor providing highdischarge pressure of more than 2 MPa.

The oilless compressor used under high pressure is expensive and poor indurability. It is free of oil. Grease-containing bearings and air sealsare short in life. So it is required to use a number of parts formaintenance, and parts used under low pressure cannot be used.

In a booster compressor in JP2000-34980A, a compressed gas is introducedin the cylinder of the compressor body and stored in the storage tank.The compressed gas in the storage tank is introduced to the compressorbody again via the bypass conduit. By repeating the compression, thecompressed gas in the storage tank is compressed gradually.

In the booster compressor, the compressed gas in the storage tank isdirectly introduced in the cylinder of the compressor body. Thus, theinside of the crank case for actuating the piston is always kept atatmospheric pressure.

As the compression step becomes high pressure, the pressure differencebetween the cylinder and the crank case increases. Especially the pistonreturns more rapidly in the reciprocating step.

Parts such as bearings for the crankshaft is subjected to more load,thereby reducing its life.

SUMMARY OF THE INVENTION

In view of the disadvantages, it is an object of the invention toprovide a multi-stage gas compressing apparatus that can be operatedunder high pressure, similar parts to those under low pressure beingused, lives of parts being extended.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will become more apparentfrom the following description with respect to embodiments as shown inaccompanying drawings.

FIG. 1 is a vertical sectional view of a booster compressor used in oneembodiment of a multi-stage gas compressing apparatus according to thepresent invention.

FIG. 2 is a block diagram showing one embodiment of a multi-stagecompressing process.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 is a booster compressor used in one embodiment of a multistagegas compressing apparatus according to the present invention.

In FIG. 1, the booster compressor 1 in this invention comprises atightly sealed crank case 2; a cylinder 3 on the crank case 2; a suckingchamber 5 having an inlet 4; and a discharge chamber 7 having an outlet6 partitioned by a wall 8 from the sucking chamber 5.

The sucking chamber 5 and the discharge chamber 7 communicate with thecylinder 3 with a sucking port 9 and a discharge port 10 respectively.The sucking port 9 and the discharge port 10 have check valves 11 and 12respectively.

In the crank case 2, a driving shaft 14 integrally connected with acrankshaft 13 driven by power is rotatably supported with bearings 15,15and a seal 16.

A connecting rod 18 is pivotally supported at one end 18 a by thecrankshaft 13 with a bearing 17.

The other end 18 b of the connecting rod 18 is mounted to a piston 19reciprocating in the cylinder 3.

To the crank case 2, an introducing conduit 20 for a compressed gas anda connecting conduit 21 are connected.

The compressed gas A is introduced in the crank case 2 through theintroducing conduit 20 and sent into the sucking chamber 5 from theinlet 4.

The compressed gas A is introduced in the crank case 2 through theintroducing conduit 20 from a plant pressure conduit system or anoilless compressor and sent in the sucking chamber 5 through theconnecting conduit 21 via the crank case 2.

The compressed gas in the crank case 2 is compressed by the piston 19reciprocating in the cylinder 3 and introduced in the sucking chamber 5.

The compressed gas A in the sucking chamber 5 is introduced in thecylinder 3 through the sucking port 9 by opening the check valve 11 withreciprocation of the piston 19. By closing the check valve 11 withreciprocation of the piston 19, the gas is compressed.

The compressed gas A is discharged from the outlet 6 via the dischargechamber 7 by opening the check valve 12 in the discharge port 10. Afterthe gas A is cooled by an aftercooler 22, it is sent to an inlet of acrank case of another booster compressor or to a storage tank.

In the embodiment, the compressed gas A is introduced from the plantpressure conduit system or oilless compressor into the sucking chamber 5via the crank case 2. At least part of the compressed gas A may beintroduced into the crank case 2 of the booster compressor 1.

FIG. 2 is a block diagram showing one embodiment of a multistagecompression process.

In the embodiment, there are a low-pressure oilless compressor 23 andtwo booster compressors 24,25 which comprises the structure whichsustains discharge pressure of compressed gas in each of the compressingsteps.

An outlet of the oilless compressor 23 is connected to an inlet of acrank case of the first booster compressor 24 via a drier 26 forremoving moisture. An outlet of the first booster compressor 24 isconnected in series to an inlet of a crank case of the second boostercompressor 25 via an aftercooler 27 for cooling the compressed gas.

A compressed gas is compressed to a discharge pressure for 1.4 MPa bythe oilless compressor 23 and introduced into the crank case of thefirst booster compressor 24 via the drier 26.

The compressed gas after cooling by the drier 26 is taken out at thedischarge pressure for 1.4 MPa.

The compressed gas compressed by the oilless compressor 23 is compressedby the first booster compressor 24 to the discharge pressure for 1.5 to2.8 MPa and introduced into the crank case of the second boostercompressor 25 via the aftercooler 27.

The compressed gas cooled by the aftercooler 27 is taken out at thedischarge pressure for 1.5 to 2.8 MPa.

The compressed gas compressed by the first booster compressor 24 iscompressed by the second booster compressor 25 to the discharge pressurefor 2.9 to 3.8 MPa and taken out.

The compressed gas compressed by the oilless compressor 23 to thedischarge pressure for 1.4 MPa is introduced in a cylinder via the crankcases of the first and second booster compressors 24,25. The dischargepressure is increased by the first booster compressor 24 to 2.8 MPa andby the second booster compressor to 3.8 MPa.

Accordingly, the pressure difference between the cylinder and the crankcases of the booster compressors 24,25 can be reduced. Compared withconventional compression by a single gas compressor, resistance againstdischarge pressure of compressed gas in each compression step can beincreased to allow operation under high pressure.

It enables load applied to parts such as bearings for the crankshaft todecrease in each compression step. Thus, their lives are increased.Parts used under low pressure can be used as well.

The foregoing merely relates embodiments of the invention. Variouschanges and modification may be made by a person skilled in the artwithout departing from the scope of claims wherein:

1. A multi-stage gas compressing apparatus comprising: a first gascompressor comprising a first driving shaft, a first crank case, a firstintroducing conduit through which a compressed gas is introduced intothe first crank case, a first driving shaft extending through the firstcrank case, a first crankshaft coupled to the first driving shaft torotate with the first driving shaft, a first connecting rod rotatablymounted at one end to the first crankshaft, a first cylinder on thefirst crankcase, a first piston coupled at the other end to the firstconnecting rod in the first cylinder to move up and down with rotationof the first crankshaft, a first sucking chamber communicating with thefirst cylinder, a first connecting conduit connecting the firstcrankcase to the first sucking chamber, the compressed gas beingintroduced from the first crank case to the first sucking chamberthrough the first connecting conduit so that the compressed gas iscompressed by the first piston in the first cylinder communicating withthe first sucking chamber; and a first discharge chamber communicatingwith the first cylinder to allow the compressed gas to be dischargedfrom the cylinder through the first discharge chamber; and a second gascompressor comprising a second driving shaft, a second crank case, asecond introducing conduit through which the compressed gas isintroduced from the first discharge chamber of the first gas compressorinto the second crank case, a second driving shaft extending through thesecond crank case, a second crankshaft coupled to the second drivingshaft to rotate with the second driving shaft, a second connecting rodrotatably mounted at one end to the second crankshaft, a second cylinderon the second crankcase, a second piston coupled at the other end to thesecond connecting rod in the second cylinder to move up and down withrotation of the second crankshaft, a second sucking chambercommunicating with the second cylinder, a second connecting conduitconnecting the second crankcase to the second sucking chamber; thecompressed gas being introduced from the second crank case to the secondsucking chamber through the second connecting conduit so that thecompressed gas is further compressed by the second piston in the secondcylinder communicating with the second sucking chamber, and a seconddischarge chamber communicating with the second cylinder to allow thecompressed gas to be discharged from the second cylinder through thesecond discharge chamber.
 2. The multi-stage gas compressing apparatusof claim 1 wherein the first and second gas compressors comprise abooster compressor.
 3. The multi-stage gas compressing apparatus ofclaim 1, further comprising an oilless gas compressor for sending acompressed gas to the first gas compressor.
 4. The multi-stage gascompressing apparatus of claim 3 further comprising an aftercoolerbetween the first compressor and the second compressor.
 5. Themulti-stage gas compressing apparatus of claim 4 further comprising adrier between the oilless gas compressor and the first boostercompressor.
 6. The multi-stage gas compressing apparatus of claim 5wherein a compressed gas is taken out of the drier, a compressed gasbeing taken out of the aftercooler, a compressed gas being taken out ofthe second gas compressor.
 7. The multi-stage gas compressing apparatusof claim 6 wherein a compressed gas of less than 1.4 MPa is taken out ofthe drier, a compressed gas of 1.5 to 2.8 MPa being taken out of theaftercooler, a compressed gas of 2.9 to 3.8 MPa being taken out of thesecond gas compressor.